Biofuel Cell: A wearable device that turns the touch of a finger into a source of power

The touch of your finger can generate power for small electronics or sensors with a new wearable device. The University of California, San Diego engineers created a flexible, thin strip that can be worn on the fingertip. It generates small amounts of electricity when someone presses or sweats on it.

This sweat-powered device generates power even when the wearer is asleep or sitting still. This could be a significant breakthrough in the field of wearables, as researchers now know how to harness the energy from sweat.

The first of this type of device has been created, according to Lu Yin (a student in nanoengineering at the UC San Diego Jacobs School of Engineering). This device is unlike other sweat-powered wearables. It does not require any physical input or exercise. This is a significant step towards making wearables more practical, accessible, and convenient for everyday people.

The new wearable energy harvester has been described in a paper published in Joule today.

Light finger pressures can also be used to generate extra power so that activities like typing, texting, and tapping in Morse Code can also be a source of energy.

Joseph Wang, a senior study author and professor of nanoengineering at the UC San Diego Jacobs School of Engineering, stated that the device could be used in all daily activities involving touch. The goal is for this wearable to work naturally for you, so you don’t need to think about it.

Most of the device’s power comes from sweat produced at the fingertips, which are 24-hour factories. The fingertips are the most sweaty area on the body. Each one contains over 1000 sweat glands and can produce as much as 100 to 1000 times the amount of sweat.

Yin stated that sweaty areas are more noticeable on the other side of the body because they don’t have enough ventilation. “The sweat that comes out of the fingertips is evaporated as soon as it reaches the air. Instead of letting the sweat evaporate, we collect it with our device, which can produce significant amounts of energy.

However, not all sweat-fueled devices can be used on the fingertip. Yin explained that it took some advanced materials engineering to collect sweat from such a small area and make it worthwhile. Researchers had to design different parts of their devices to absorb and convert effort into electrical energy.

Yin collaborated with UC San Diego’s nanoengineering Ph.D. student Jong-Min Moon and Juliane Sepionatto on this project as part of a team that included Wang, also director of the Center for Wearable Sensors. Eight years ago, Wang and his team were the first to develop sweat-powered wearables. They have continued to improve on this technology ever since, creating new and better ways for wearables to be powered by sustainable sources such as their wearers and the environment.

The latest energy harvesting technology is unique because it can be used anywhere. It is not limited by solar cells or thermoelectric generators, which work only when there’s a significant temperature difference between the surrounding and the device.

How it works

The flexible, thin strip can be wrapped around your fingertip in a Band-Aid style. Carbon foam electrodes are used to absorb sweat and transform it into electricity. Enzymes are embedded in the electrodes to trigger chemical reactions between sweat molecules and lactate. This creates electricity. A chip that’s made from a piezoelectric material is under the electrodes. This generates additional electricity when it’s pressed.

The electrical energy is stored in a small capacitor and released to other devices as needed.

Researchers had the subject wear the device on one fingertip while doing sedentary tasks. The device accumulated almost 400 millijoules (enough to power an electronic watch for 24 hours) over 10 hours of sleep. The device earned nearly 30 millijoules of energy after one hour of simple typing, clicking on a mouse, and clicking a button.

This is only one fingertip. Researchers found that securing devices to the rest of the fingertips would produce ten times more energy.

This technology gives users a net energy gain by using sweat at the fingertip. It flows naturally, regardless of where or what you’re doing. Wang said that this is the maximum energy return on your investment.

Yin explained that this is similar to a device that uses energy when you exercise. Running costs hundreds of joules, and the device will only generate millijoules. Your energy return on investment will be meager in this case. This device, however, will give you a very high return. You are not working when you’re asleep. You only invest about half a millijoule even if you press one finger.

The researchers also connected the energy harvester to an electronic device consisting of a chemical sensor and a low-power display that shows the numerical readings of the sensor’s data. The energy harvester could be powered by pressing it ten times per 10 seconds or being held onto the fingertip for 2 minutes. The researchers connected their device to a vitamin C sensor they had developed in the laboratory. The researchers had the subject take a vitamin-C pill and then use their finger-powered system to read their vitamin-C levels. The researchers also demonstrated that the system could measure the sodium ion concentration of saltwater solutions using a lab-made sodium sensor.

Yin stated, “our goal is to make it a practical device.” We want to prove that this isn’t just another excellent device that generates a little energy and can power functional electronics like sensors and displays.

The team is working to improve the device’s efficiency and durability. Future research will combine the device with other energy harvesters to create new self-powered wearable devices.